The specific aims include: (1) Determination of the biological phenotype (tropism, replication and syncytium-forming ability of the isolates) of HIV-1 isolates obtained around seroconversion in individuals who acquire HIV infection through heterosexual contact. (2) Genotypic characterization of the isolates. Specifically sequence variation in the envelope gene within and between individuals will be carried out and (3) Determination of the infectivity and replicative ability in langerhans cells of HIV-1 isolates obtained early after infection from subjects infected heterosexually.